1. Field of the Invention
The present invention relates to an image sensor, and more particularly, to an image sensor and a method for fabricating the same in which a partial light-shielding layer is additionally arranged on a path of a particular colored light, for example, a red colored light that may cause excessive permeation, to partially shield the corresponding red colored light in a state that a red colored light, a green colored light, and a blue colored light are permeated into each photodiode of a semiconductor substrate, so that the permeation position of the red colored light coincides with that of the green colored light and the blue colored light each having the wavelength shorter than that of the red colored light, thereby normally generating optical charges caused by the red colored light in an effective depletion area of the photodiode like those caused by the green colored light and the blue colored light.
2. Discussion of the Related Art
Recently, with rapid development of the electric and electronic technology, various electronic appliances such as video cameras, digital cameras, personal computers with a small sized camera, and cellular phones with a small sized camera have been widely spread.
A charge coupled device (CCD) has been typically used as a related art image sensor. However, the CCD has several drawbacks in that a high driving voltage is required, an additional circuit is required, and the process cost is high. For these reasons, the use of the CCD is on a decreasing trend.
As an example of an image sensor that can substitute for the CCD, a complementary metal oxide semiconductor (CMOS) image sensor has received much attention recently. Since a CMOS image sensor is based on a CMOS circuit technology, it has advantages in that low voltage driving is available, no additional circuit is required, and the process cost is cheap unlike the CCD.
As shown in FIG. 1, the related art CMOS image sensor, i.e., a CMOS image sensor for displaying color images includes photodiodes 30 formed on a semiconductor substrate 40, generating and storing a series of optical charges from externally input lights L, and a color filter array CA coloring the externally input lights and transferring the colored lights to the photodiodes 30. In this case, an intermediate layer 20 is interposed between the color filter array and the photodiodes 30 so as to transfers the lights, which have transmitted the color filter array CA, to the photodiodes 30.
As shown, the color filter array CA includes a structure of a plurality of unit color cells C1, C2 and C3 with red, green and blue in combination (four color cells are shown in FIG. 1).
In this state, the red color cell C1, the green color cell C2, and the blue color cell C3 color the externally input lights in red, green and blue, and transfer the colored lights to the photodiodes 30. The respective photodiodes 30 corresponding to the red color cell C1, the green color cell C2 and the blue color cell C3 one to one generate and store the colored lights, i.e., optical charges corresponding to red colored light, green colored light and blue colored light.
Afterwards, signal processing transistors (not shown) adjacent to the respective photodiodes 30 transfer/discharge the optical charges generated and stored by the corresponding photodiodes 30 to an interpolation circuit (not shown). The optical charges are displayed in color images of uniform resolution by interpolation procedure through the corresponding interpolation circuit.
Under the related art CMOS image sensor system, the red colored light has a wavelength of 600 nm to 700 nm longer than the blue colored light having a wavelength of 400 nm to 500 nm and the green colored light having a wavelength of 500 nm to 600 nm. Therefore, as shown in FIG. 2, the red colored light which has transmitted the red color cell C1 is excessively permeated into the semiconductor substrate 40 in comparison with the green colored light which has transmitted the green color cell C2 and the blue colored light which has transmitted the blue color cell C3. If the red colored light is excessively permeated into the substrate 40, optical charges e1 caused by the red colored light are not generated normally in the effective depletion area DA of the photodiodes 30 unlike optical charges e2 and e3 caused by the green colored light and the blue colored light. That is, the optical charges e1 caused by the red colored light are generated abnormally spaced apart from the effective depletion area DA. Under the circumstances, if no separate step is taken, the optical charges e1 transferred/discharged to the interpolation circuit by the signal processing transistors are relatively smaller than the other optical charges e2 and e3. For this reason, the color images finally obtained by the interpolation circuit do not have a normal ratio of 1:1:1 with red, green and blue, thereby causing low display quality in color and resolution.